Per L2 naughty "out of family" sensor that scrubbed the SpaceX Falcon 9 NROL-76 launch was a TOTO (Temperature Ox Tank Outlet) sensor. They had redundancy, but didn't want to risk losing another one, so the "abundance of caution" was as presented.

It's not obvious to me why they are worried about losing another such TOTO sensor. If they have a redundant sensor, they know the temperature pre-launch. And once it's in flight, it should not matter if the sensor fails, since there is nothing they can do about it anyway.

The only way I can see this being useful at all during flight is if they use it to optimize fuel usage or mixture adjustment. But as far as I know, this is normally done by volume remaining in the tank. They would want both tanks to run out at the same time, independent of the exact temperature of the LOX.

I don't agree. My rebreather has three oxygen sensors monitored by one computer and a fourth (identical) one monitored by a fully independent second computer. All monitoring the exact same thing - O2 partial pressure. If one of the three read out of range the computer votes it out of the system.

However - what if two read the same and are both wrong? Then the good sensor gets voted out and basically you die. It's a common occurrence. O2 cells from the same batch, mechanical shock, moisture contamination, etc.

Point being, they may not know which sensor is giving bad readings. It's not worth betting the company on.

(By the way, in rebreathers you have to assume the rig is always trying to kill you and you have to use the computer in your head to make the right decisions. I'm very keyed into the danger of assumption)

Your example is valid only if the F9 computer uses the readings to make changes in flight which we don't know and Lou clearly mentions that his assertion is only on the assumption that it's not being used.

If the F9 doesn't do anything with the sensor readings than I think Lou's assertion makes sense and your example doesn't apply. IMHO

SpaceX has lost two stages to O2 tank overpressure events in the last couple years ... do we *REALLY* think any of us kibitzing on the sidelines has insight into the nuts and bolts of the today's sensor-related scrub and whether it was necessary?

SpaceX has lost two stages to O2 tank overpressure events in the last couple years ... do we *REALLY* think any of us kibitzing on the sidelines has insight into the nuts and bolts of the today's sensor-related scrub and whether it was necessary?

(fan hat) Yeah, let's not second guess... it's not that exciting. ... note which hat. But yeah.

Logged

"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

This explains why SpaceX had to apply to the FCC for spectrum for what would otherwise have been an NSS launch. So, this tracks similar to CRS launches. NASA is the end-user, but the launches are treated as a commercial space launch. Here, NRO is the end-user, but the launch is actually a commercial launch for Ball. So, they need FAA launch license and FCC STA. If the DoD had been the direct client (via NRO), the DoD would have ceded authority and spectrum directly.

SpaceX has lost two stages to O2 tank overpressure events in the last couple years ... do we *REALLY* think any of us kibitzing on the sidelines has insight into the nuts and bolts of the today's sensor-related scrub and whether it was necessary?

I mean, are we seriously discussing this?

Sure. It's called engineering, as opposed to knee-jerk reactions. Commercial air flights, where people's lives are at risk, often take off with broken sensors. There is a "minimum equipment list" of stuff that has to be working at takeoff. If it's not on that list you can go with it inoperative.

This is exactly the same idea applied to rockets. Instead of a pre-defined list, a group of engineers decides whether it's safe to go. If it's OK you proceed. Note that this happened four times on the last Atlas launch alone.

Atlas LOX pump sensor not working properly. Anomaly team being convened.

plus a LOX leak, an erratic voltage indication, and poor signal to the range.

So it's perfectly reasonable to ask (not second guess) why this sensor failure makes it better to scrub. And scrubbing, too, has risks, at the very least an extra drain-fill cycle (which is precisely what caused problems before). So SpaceX must believe, or at least intuit, that proceeding as is had more risk than scrubbing. The question is why?

On the face of it based on the little information we have that sentence doesn't seem to add up. that's it.

Sure it does. "another one" is the sensor...

In aviation for some systems, if you have a triply redundant system you can go if you lose one, as long as you still have two. For other systems, no. For rockets, losing a sensor is an almost automatic stop the process.

Logged

"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

On the face of it based on the little information we have that sentence doesn't seem to add up. that's it.

Sure it does. "another one" is the sensor...

In aviation for some systems, if you have a triply redundant system you can go if you lose one, as long as you still have two. For other systems, no. For rockets, losing a sensor is an almost automatic stop the process.

You are 100% correct, provided the system is needed during flight and a failure of that system during flight would cause a LOM

On the face of it based on the little information we have that sentence doesn't seem to add up. that's it.

Sure it does. "another one" is the sensor...

In aviation for some systems, if you have a triply redundant system you can go if you lose one, as long as you still have two. For other systems, no. For rockets, losing a sensor is an almost automatic stop the process.

You are 100% correct, provided the system is needed during flight and a failure of that system during flight would cause a LOM

Is that the case here?

I hope by the time I log in again this will be irrelevant.

Help me grasp this, how is this worthy of discussion? What is so difficult to understand here? They have a requirement for double redundancy. They lost a sensor, so now that requirement is no longer met. Thus a scrub.

What is it you need explained? Or are you fishing for something else, that "SpaceX is doing systems engineering wrong" and need to do X and Y? If so start a thread about it in the SpaceX general forum.

... air flights, where people's lives are at risk, often take off with broken sensors. There is a "minimum equipment list" of stuff that has to be working at takeoff. If it's not on that list you can go with it inoperative.

Yeah. I was once in a cockpit when the pilot checked his stuff. He said "ooops", then hit the dash hard with his fist, and a few seconds after that said "good". Totally reassuring.

So let's recap what we know about the satellite:- goes to LEO, 51° inclination- built by Ball- launch procured by Ball- contract probably awarded in 2013 (per DNRO remarks to Congress)

What is unknown:- weight (for LEO, RTLS is possible even with relatively heavy payloads)- orbital altitude- role of the satellite

Regarding the role of the satellite, based on previous NRO launches it's either comms, SIGINT, optical observation or radar observation.Ball's specialty is optical instruments: they built Worldview 1, 2, and 3, Kepler, and optical instruments for many NASA missions. So if the NRO ordered a satellite in a fixed-price bid (as Ball procuring the launch seems to suggest), Ball probably won because it was in its area of expertise, namely optical payloads. So it's likely an optical observation sat.

However, 51° inclination is weird for an optical satellite. It could be a non-sun synchronous mission which aims at acquiring data at different times of the day. It could be a high-altitude (for LEO) satellite for more persistent surveillance, in which case 51° could be enough to image most interesting areas. Ball has been working on just that, a telescope with membrane optics called MOIRE (http://www.ball.com/aerospace/programs/moire), so it could be a demonstrator for that before a full mission in GEO.

Note the USA 193 orbit was also weird: 349 km × 365 km × 58.48° makes regions above 60° inaccessible, so Northern Russia could not have been imaged with that orbit.